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i.'UV 2 T 


° f the HARVARC 


The University of Kansas 
Lawrence, Kansas 

NUMBER 106, PAGES 1-37 NOVEMBER 10, 19S3 



K. N. Whetstone 1 and P. J. Whybrow 2 

For many years most vertebrate paleontologists regarded the 
crocodilians as a stable side-branch of the archosaurian reptiles, 
of interest because of their supposedly primitive structure and their 
relationship (albeit “distant”) to the dinosaurs and birds. Recent 
studies by A. D. Walker (1968, 1970, 1972, 1974) and E. Buffetaut 
(1979) have rekindled interest in the crocodilians as a morpho- 
logically diverse group with terrestrial, marine and amphibious 
specializations. The extent of this diversity is illustrated by Walker’s 
arguments (1972, 1974) that early crocodilians were close to the 
basal stock of birds. 

Prior to this report, our knowledge of the earliest (Triassic) 
crocodilians was based upon at least fifteen published specimens, 
assigned to six genera. While this fossil record is by no means 
meager, it is very poorly known, particularly in the anatomical 
details which are important in phylogenetic and functional studies. 
This lack of knowledge is partly the result of the poor preservation 
of the material and the difficulties of preparing it from indurate 
sandstones and ironstones. 

In 1966 and 1967 a joint British Museum (Natural History) — 
London University expedition recovered a partial crocodilian skele- 
ton from Upper Triassic sediments in Lesotho, southern Africa. 
The fossil is of a lightly built individual with a suite of adaptations 
for rapid terrestrial locomotion. As a result of its detailed preserva- 

1 University of Kansas and Museum of Natural History, Lawrence, Kansas; 
present address: Union Texas Petroleum, 2500 First Oklahoma Tower, Okla- 
homa City, Oklahoma. 

2 British Museum (Natural History), London, England. 



tion, it is possible to describe many features that are strikingly 
different from those of Recent crocodilians. These characters pro- 
vide new support for Walkers hypothesis of a close relationship 
between birds and crocodilians and further expand our knowledge 
of the morphological diversity of the Crocodylia. The new Lesotho 
specimen is distinct from the genus Orthosuchus and is assigned 
to the new genus and species, Lcsothosuchus charigi. 

The type specimen was collected and prepared by P. J. Why- 
brow, whose contribution is acknowledged by the joint authorship 
of this paper. The text which follows is by the senior author, who 
takes full responsibility for the interpretations presented. 


The first Triassic reptile to be correctly recognized as a croco- 
dilian was Notochampsa istcdana from Cape Province, South Africa 
(Broom, 1904). The type material of this species has never been 
prepared from the matrix. As exposed, it consists of an impression 
of the nasal and temporal regions of the skull (Fig. 1A), part of 
the right mandible, a right pectoral girdle with the glenoid partly 
covered, the proximal end of the right humerus, parts of the left 
forelimb, parts of the left hindlimb (figured by von Iluene, 1925), 
and impressions of the dorsal armor. Notochampsa longipes, de- 
scribed by Broom (1904) in the same work, was later selected by 
Ilaughton (1924) as the type species of his genus, Erythrochampsa. 
The type specimen has been figured by Nash (1971). It consists 
of dorsal and ventral osteoderms, both ischia, a right pubis, a possi- 
ble left pubis, the metatarsus, a tibia, and a fibula. Von Iluene 
(1925) identified a radius, ulna, and femur in the block, but these 
are not evident in Nash’s photographs. An additional, fragmentary 
specimen was referred to this species by Broili and Schroeder 
(1936). Although the genera Notochampsa and Erythrochampsa 
can be confidently assigned to the Crocodylia, their type material 
is indeterminate. Owing to their poor preservation and description, 
it would be possible to assign any of the other Triassic forms to 
those taxa by attributing the few discernable differences to inade- 
quate representation and fault}' preservation. For the present, both 
Notochampsa and Erythrochampsa are best considered nomina 

A single specimen of a crocodilian from Triassic sandstones of 
the Connecticut valley, named longipes by Emerson and Loomis 
(1904), was referred bv them to Stcgomus but was later given its 
own genus, Stcgomosiiclws , by von Iluene (1922). It, too, is 
poorly preserved, although a good impression of the skull roof, 
dorsal armor, and metatarsals can be found on the counterslab. 



Walker (1970) argued its crocodilian affinities and attempted a 
cranial reconstruction based upon a cast of the counterslab. I have 
examined this cast and agree that Stegomosuchus is a crocodilian. 
An expanded squamosal with a longitudinal ridge and a flange on 
the lateral margin are distinctive crocodilian features. There also 
appears to be a posterior palpebral element preserved on the right 
postorbital. Unfortunately, the preservation is too incomplete to 
determine other details of the skull roof with any confidence. An 
outline of the limbs is given by Emerson and Loomis (1904), but 
only the metatarsals appear as relief on the casts. Lacking details 
of skull construction, limb girdles, appendages, and vertebral col- 
umn, Stegomosuchus can only be classified as a crocodilian of un- 
determined affinity, probably of protosuchian grade. 

The first Triassic crocodilian to be represented and described 
in detail was Protosuchus richardsoni (Fig. IB); first named by 
Brown (1933, 1934) and later monographed by Colbert and Mook 
(1951). Most of the skeleton is preserved in the type (AMNH 
3024), although there are several other specimens, all from the 
Dinosaur Canyon Sandstone in Arizona, U.S.A. Also represented 
by good material is Orthosuchus stormhergi (Fig. 1C), known by 
two specimens from Lesotho which were described by Nash ( 1968, 
1971, 1975). As originally restored by Colbert and Mook, Proto- 
suchus differed substantially from Orthosuchus in having no antor- 
bital fenestra, the parietal excluding the frontals from the upper 
temporal fenestrae, the dentarv notched posteriorly and the quad- 
rate unfenestrated. These differences at first seemed sufficient to 
place them in separate families, but a new specimen of Protosuchus 
described by Crompton and Smith (1980) resolved some of the 
discrepancies. Protosuchus is now known to have an antorbital 
fenestra and a pneumatic quadrate. In the classification that fol- 
lows. I have placed Orthosuchus and Protosuchus in the same fam- 
ily, Protosuchidae. 

The new Lesotho specimen is distinct from Orthosuchus at the 
generic level, but is placed with it in the new subfamily, Ortho- 
suchinae for reasons discussed below. In previous studies by Nash 
(1971. 1975) and Whetstone and Martin (1979), the Lesotho speci- 
men, heretofore unnamed, was referred to the genus Notochampsa. 
Walker (1972) mentioned the specimen by number only. Lesotho- 
suchus and Orthosuchus were small animals with more or less 
gracile build. Terminal length for both taxa was undoubtedly less 
than one meter. 

Eopneumatosuchus colhcrti is a crocodilian recently described 
by Crompton and Smith (1980). It is known only by a skull col- 
lected from sediments of probable Upper Triassic age in Arizona. 
It is characterized by the highly pneumatic construction of the 



braincase and an elongate laterosphenoid. I have placed it in its 
own subfamily of the Protosuchidae. 

Numerous other taxa liave been associated with protosuchian 
crocodilians at one time or another. These include Dyoplax , Erpeto- 
sucliiis , Hesperosuchus , Proterochampsa , Saltoposuchus , Pedetico- 
sciiirns , Microchampsa , Platyognathus , Sphenosiichus , Pseudhespero- 
su chits , Hemiprotosuchus , and an unnamed form from Welsh 
fissure deposits (Kermack, 1956; Crush, MS.). Of these, Krebs 
(1976) considered Dyoplax , Erpetosuchus , Hesperosuchus , Protero- 
champsa, , and Saltoposuchus to be thecodontians of little or no 
relation to the Crocodylia. Pedetlcosaurus and Microchampsa are 
based on insufficient material to be confidently assigned to any 
particular archosaur group. Platyognathiis is known principally 
from a referred specimen (Simmons, 1965), which is much too 
fragmentary to support Simmons’ conclusion that it had a meso- 
suchian palate. The coracoid does appear to be elongated, how- 
ever, and this might indicate crocodilian relationships. The teeth 
have expanded roots, but are serrated. Until more complete 
material is known, the best assignment for Platyognathus is “PCroco- 

The remaining taxa, Sphenosiichus , Pseudhesperosuchus , Hemi- 
protosuchus and the unnamed Welsh genus can be loosely grouped 
into the Sphenosuchidae. As discussed below, they share some 
diagnostic features with “true” crocodilians, but are very primitive 
in other respects. To include them in the Crocodylia would greatly 
modify traditional interpretations of that group, diminish the diag- 
nosis, and possibly create a grade taxon from a demonstrably 
monophyletic (sensu Hennig, 1966) one. On the other hand, it 
seems advisable to remove them from the Thecodontia. In informal 
nomenclature I have followed Walker (1970) in using the name, 
croeodylomorphs to designate the true crocodilians plus the Spheno- 
suchidae. In the formal classification which follows, the spheno- 
suchids appear as the “sister-group” to the crocodilians. All of the 
sphenosuchids (with the possible exception of Hemiprotosuchus) 
have an unusual coracoid morphology which can either be inter- 
preted as uniquely derived for the group or primitive for the croco- 
dvlomorphs. This feature may link them to Hesperosuchus if 
Colbert’s (1952) “problematical bone” of Hesperosuchus is really 
a coracoid. 

The following classification is used in this study. Despite the 
unsettled nature of archosaur taxonomy and the reluctance of 
many workers to include birds within the Archosauria, I have re- 
jected a traditional “grade” classification of archosaurs. Taxa which 
I believe to be paraphyletic grades are indicated by quotation 
marks and the plesion convention of Patterson and Rosen (1977) 
is used to eliminate an unnecessary higher taxon. 



Division Archosauria 

Subdivision Nidosuchia, new taxon 

Plosion Sphenosuchidae: Sphcnosuchus , Pscudhcspcrosuchus, Welsh 
fissure deposit crocodylomorph, 
?Hcspcrosuchm, PHemiprotosuchus 

Infradivision Crocodylia 

Crocodylia, insertae sedis (“Protosuchia”) 

Family Protosuchidae: 

Subfamily Protosuchinae: Protosuchus 
Subfamily Eopneumatosuchinae: Eopneumatosuchus 

Subfamily Orthosuchinae: Orthosuchus, Lesothosuchus 
“Protosuchia” indet.: Stegomosuchus 

Notochampsa (nomen dubium), 
Enjthrochampsa (nomen dubium) 
Order Mesoeucrocodylia, new taxon 

Mesoeucrocodylia, insertae sedis ( “Mesosuchia” ) 

Suborder Eusuchia 
Infradivision Aves 


Division Archosauria 
Infradivision Crocodylia 

Family Protosuchidae 
Lesothosuchus new genus 
Lesothosuchus charigi new species 

Diagnosis: Small crocodilian with relatively long limbs; postorbital 
with a facet for a supraorbital (palpebral) bone; temporal fenestrae 
moderate in size and pear-shaped; squamosal broad, with a longi- 
tudinal ridge near the lateral margin; paroccipital process centrally 
placed, relatively short and broad; carotid artery enclosed by bone 
posterior to the otic region; squamosal overhangs the tympanic 
cavity; braincase sutures to the quadrate anteriorly, retains a cotyle 
posteriorly; quadrate hollow and highly fenestrated; periotic pneu- 
maticity developed; floccular recess present within endocranium; 
lower temporal fenestra reduced; vertebral centra platycoclous ex- 
cept the posterior caudals; coracoid elongate, expanded sternally, 
and “waisted”; humerus with an expanded, convex head; ulna with 
two proximal cotyles and a rounded, convex articulation for the 
radius; dorsal armor finely sculptured. 

Derivatio nominis: generic name recognizes the provenance of the 
type specimen; species name in honor of A. J. Chari g who has 
contributed much to our knowledge of early archosaurs. 

Type: BMNH RS503 (Table 1); left otic and temporal region of 
skull; left dentary; one cervical, two dorsal, and two caudal verte- 
brae; a caudal chevron; some rib fragments; dorsal end of the right 



scapula; right coracoid; right and left humeri; a left ulna; most of 
left femur; distal end of right femur; a right fibula; right and left 
metatarsals of the second digit; two phalanges from the pes; several 

Type locality: Lithipeng South, Mohales Hoek district, Lesotho; 
from northwest face of vertical slope at longitude 24°44' and lati- 
tude 30°19'S. 

Horizon: Red Beds of Stormberg Series, just below Cave Sand- 
stone; photograph in Charig (1969) shows stratigraphy of the 



The left dentary and most of the left half of the posterior por- 
tion of the skull are preserved. This includes the skull roof, occiput, 
otic capsule, parocciput, the dorsal surface of the quadrate and 
part of the postorbital bar. The basieranium is missing. 

The dentary (Fig. 6A,B) is a thin, slender bone with alveoli 
for eight or nine teeth preserved. The bony tooth sockets are 
completely separated by bone to the rear of the tooth row. In 
Recent erocodilians the posterior mandibular teeth of juveniles are 
set in a groove. As the individual grows the groove is progressively 
divided into alveoli from the front to the rear. The dentary be- 

Table 1. — Measurements in mm for Lesothosuchus charigi (BM (Nil) R 8503). 

Temporal width 

Width across 





Anterior height 

Anterior Anterior 

to top of 



Length neural canal 

Cervical centrum 










Anterior caudal 





Posterior caudal 





Max prox Max dist 




width width 





12.6 11.1 





9.1 6.5 




70 est.* 

? 15.1 





8.0 7.2 



* Skull widths are doubled measurements to midline; anterior cervical measure- 
ments include keel; femur length is conservatively estimated by reconstruc- 
tion of the proximal end based upon comparison with Triassic and Recent 
taxa; distal fibula may be somewhat crushed. 


comes fully septate only in specimens which are near “terminal” 
size. Fully septate dentaries are found in the type specimens of 
both Lesothosuchus and Orthosuchus. If Triassic crocodilians de- 
veloped as Recent ones do, this indicates that the type specimens 
are adults, that their small size cannot be attributed to youth, and 
that the differences in skeletal proportions between the types do 
not represent ontogenetic variation in a single species. 

There are two grooves on the internal surface of the dentary, 
just ventral to the tooth row. The more dorsal of these becomes en- 
closed anteriorly to form the alveolar canal. The ventral groove 
held the anterior extension of the 1 angular bone which formed the 
floor of Meckel’s canal. Behind the ventral groove at the postero- 
ventral corner of the dentarv is a rounded surface for articulation 
with the angular. Although there is no broad, rugose articular sur- 
face of the sort that is found in Alligator , there probably was some 
lateral exposure of the angular bone in this area. 

The dentarv is highly sculptured anteriorly, but less so pos- 
teriori}’. At the posterior end, there is no notch for the mandibular 
foramen. This notch is also absent in Orthosuchus, but, to the 
best of my knowledge, in no other crocodilians. In Orthosuchus, 
Nash restores the mandibular foramen as being posteriorly posi- 
tioned and quadrangular, also unique among the Crocodylia. 

The skull roof of Lesothosuchus is strongly sculptured with ir- 
regular pits and ridges (Fig. 2A). The anterior roofing elements 
preserved are the dorsal portion of the postorbital (Fig. ID) and 
a fragment of the frontal. The postorbital bone forms the back of 
the orbit, part of the skull roof, and the anterior margins of the 
upper and lower temporal fenestrae. In eusuchian crocodilians, 
the postorbital is indented on its anterolateral surface so that the 
anterolateral corner of the temporal skull roof overhangs the cheek 
at the back of the orbit. This indentation is not developed in Leso- 
thosuchus or other protosuchian crocodilians. However, both 
Orthosuchus and Lesothosuchus have the postorbital indented pos- 
teriorly so that it forms part of the shelf which covers the otic re- 
gion. At the posterior corner of the orbit the postorbital has a 
shallow, crescent-shaped depression. In Orthosuchus this depres- 
sion receives the posterior palpebral, or supraorbital bone. In Re- 
cent crocodilians, these dermal elements are loosely attached to 
the cranium. They are rarely preserved in their natural position 
in fossils. Extant forms have only a single, anterior supraorbital 
attached to the prefrontal and lacrymal. Orthosuchus, Lesotho- 
suchus, Protosuchus (see Walker, 1970; Crompton and Smith, 19S0), 
and Stegomosuchus appear to have been unique in having an addi- 
tional posterior element. Since a posterior papebral bone occurs in 
all of the accepted Triassic taxa, we presume this to be the primitive 



condition in the Crocodylia. Better material of sphenosuchid skulls 
could serve as an “outgroup” comparison to test this polarity. 

Most of the preserved portion of the skull roof is formed by 
the squamosal bone, which extends laterally to overhang the otic 
region. The squamosal, postorbital, parietal, and, probably, the 

Figure 1. — Restorations of the dorsal aspect of the posterior skull roof in 
A, Xotocliainpsa istedana after von Iluene (1925); B, Protosuchus richardsoni 
after Colbert and Mook ( 1951); C, Orthosuchas stormbergi after Nash (1975); 
D, Lcsothosuchus charigi, BM (NH) R 8503. Seale is 2 cm. 



frontal form the dorsal margins of the superior temporal fenestra. 
The fenestrae are moderate in size and pear shaped, in contrast to 
the large, rounded fenestrae of both specimens of Orthosuchus, 
and to the small, oval fenestrae of the type specimen of Noto- 
champsa (Fig. 1). Stegomosuchus, however, is quite similar in 
this region. The size, shape and position of these openings vary 
ontogenetically in living crocodilians (Nash, 1971), but appear to 
be a useful taxonomic indicator when individuals of a similar size 
are compared. 

As in all crocodilians, the parietal of Lesothosnchus is a median, 
unpaired element. This is in contrast to the paired parietals of 
typical proterosuchian and pseudosuchian archosaurs. There is no 
pineal opening. The posterior portions of the frontals arc probably 
preserved on the specimen, but I have been unable to locate a 
fronto-parietal suture. 

The parietal extends posteriorly onto the broad occipital surface 
of the skull (Fig. 2C). As is characteristic of the Crocodylia, the 
occiput slopes abruptly downward from the skull roof. The occiput 
is formed by the parietal, squamosal, supraoccipital and otoccipital 
(fused exoccipital/opisthotic) bones. The parietal contributes only 
a small, centrally situated process to form the top of a central crest. 
On either side of this crest are impressions for the insertion of 
cervical musculature onto the supraoccipital. The parietal and 
supraoccipital form the dorsal and ventral margins of the small 
posttemporal fenestra. This fenestra leads into a small pneumatic 
sinus, which, in turn, connects with the tympanic cavity and the 
superior temporal fenestra. In modern crocodilians the occipito- 
temporal artery passes along the roof of the dorsal pneumatic cavity 
and through the posttemporal fenestra (Hochstetter, 1906). A simi- 
lar course is indicated for Lesothosnchus . 

The squamosal extends ventrally onto the dorsolateral corner 
of the occiput. On the occipital surface I have been unable to trace 
the suture with the otoccipital beyond the lateral-most margins. 
On the tympanic surface the suture is squamous, extending much 
farther ventrally. 

Most of the occipital surface of Lesothosnchus is formed by 
the otoccipital which extends laterally and ventrally from the supra- 
occipital to surround most of the foramen magnum. On either side 
of the foramen magnum it forms a lateral (paroccipital) process, 
ventrally situated at about the level of the otic capsule (Fig. 3A). 
This process is relatively short and is preserved only as a thin 
sheet. Except for the area at its base, it is completely free of the 
overlying squamosal. This contrasts with the primitive archosaurian 
condition found in most theocodontians and dinosaurs, in which 
the paroccipital process is long and dorsally placed. The squamosal 
overlies it for most of its length (either arching over it to form a 





large post-temporal fenestra or suturing along its antero-dorsal 
margin) and curves downward near the lateral terminus to form 
a socket for the dorsal knob of the quadrate. In some ways, the 
paroeciput of cusuchians resembles theoeodontians more closely 
than Lesothosuchus — the paroeciput is long, dorsally situated and 
underlies the squamosal, which articulates with the quadrate just 
anterior to the lateral terminus of the paroeciput. 

In Lesothosuchus the otoccipital also forms the dorsal and lat- 
eral margins of the foramen magnum and the lateral portion of the 
occipital eondvle. The central portion of the eondyle, presumably 
formed by the basioccipital, is not preserved in the type specimen. 
Immediately lateral to the eondyle is a groove leading into a dor- 
sally directed foramen which marks the exit of the vagus nerve 
from the cranium. Lateral to this are one or more additional fora- 
mina, which are badly crushed. One of these must be the carotid 
foramen since it overlies a bony tube which corresponds in posi- 
tion to the carotid eanal of Recent taxa. Croeodilians are unusual 
among diapsid reptiles in having the carotid artery enclosed by 
bone before it enters the ear region. 

The otie region of the cranium is particularly well preserved 
(Figs. 2B,D; 3). It is roofed by both the squamosal and postorbital. 
The postorbital is broad and is greatly indented behind the post- 
orbital bar. On its ventral surface it bears a pit for the dorsal head 
of the laterosphenoid. This type of laterosphenoid articulation is 
widely distributed among the arehosaurs, occurring in Recent eroe- 
odilians, ornithisehian dinosaurs, and Mesozoic hesperornithiform 
birds, for example. In the latter group the laterosphenoid articu- 
lates with the postorbital process of the frontal bone. 

The squamosal broadly overhangs the otie cavity, dorsal and 
posterior to the squamosal articulation with the quadrate bone. 
On the dorsal surface of the squamosal near the lateral margin is 
a sinuous longitudinal ridge bordered laterally by a shallow groove. 
In Recent croeodilians this ridge and groove represent the attach- 
ment for the thickened integument that extends ventro-laterally 
over the muscular operculum (Ohrklappe). On this basis we can 
infer an opercular structure for Lesothosuchus. In Recent taxa this 
external ear receives blood supply from a branch of the temporal 
artery, which exits the dorsal periotic sinus laterally ( Iloehstetter, 
1906). There is some evidence for the presence of this arterial 
supply in Lesothosuchus , where a series of grooves radiate out- 
ward from a foramen near the squamosal/ prootie/ otoceipital junc- 
ture (the foramen is described below as the lateral opening of the 
dorsal periotic sinus). Lesothosuchus differs from eusuehians in 

Figure 2. — Lesothosuchus chart gi, BM (NH) R 8503; skull in A, dorsal; 
B, lateral; C, posterior; D, ventral views. Scale is 2 cm. B and D are stereo- 



lacking a thickened ventral lip for the attachment of the operculum 
and from Orthosuchus and eusuchians in having the lateral margin 
of the squamosal only weakly downturned. 

The quadrate is preserved in an approximately natural position. 
It is strongly inclined, but less so than in eusuchians. The anterior 
end extends far medially to suture with the squamosal, prootic, 
postorbital, and laterosphenoid, all of which comprise the facies 
articularis anterior. In this region, the quadrate of eusuchians su- 
tures with these same bones and also with the parietal. In Lesotho- 
suclius there may be some slight contact with the parietal at the 
rear of the superior temporal fenestra, but it would be negligible. 

Figure 3 . — Lcsothosuchus charigi , RM (Nil) R 8503: skull in A, lateral 
and B, ventral aspects; key to Figure 2 R, D. Sq, squamosal bone; Pro, prootic, 
Oto, otoceipital; Qu, quadrate; ant. pneu., antrum pneumatieum, fac. artic. 
post., facies articularis posterior. In Fig. A the quadrate is shaded; in Fig. B 
the pneumatic cavities and foramina are shaded. 



The quadrate forms part of the lateral wall of the fenestra, curving 
dorsallv to be applied as a thin sheet along the medial margins of 
the squamosa] and postorbital. The anterior end of the quadrate 
is compressed dorso-ventrally, restricted to the area dorsal to the 
rostral periotic sinus. This is in striking contrast to the anterior 
process of cusuchians, which extends ventrally to contact the basi- 
cranium, in some cases incorporating a pneumatic sinus. Major 
modifications of this sort occurred throughout the otic region of 
eusuchians as a result of the increased area of fixation for the 
akinetic quadrate. 

Lesothosuchus resembles mcsosuchians and eusuchians in hav- 
ing an additional articulation for the quadrate at the rear of the 
tympanic cavity, the facies articularis posterior (Fig. 3). While 
eusuchians have a sutural contact here, Lesothosuchus retains a 
cotyle for the quadrate, the first record of such a primitive articu- 
lation in a crocodilian. The presence of a cotyle here does not in- 
dicate streptostyly, which is precluded by the anterior suturing 
of the quadrate to the braincase and skull roof. It does, however, 
provide an intermediate between the loosely articulated quadrates 
of generalized theocodontians and sphenosuchids and the fixed, 
extensively sutured quadrates of mesosuchians and eusuchians. 

The articular cotyle is supported by two processes (Fig. 3B). 
The posterior process originates just anterior to the paroeeipital 
process and is undoubtedly part of the otoccipital bone. The an- 
terior process is closely associated with the posterior part of the 
otic capsule and cochlear canal and is probably also part of the 
otoccipital. There is no clear separation of the prootic and otoc- 
cipital in this area, and it is also possible that the prootic forms 
part of the cotyle, as suggested by Whetstone and Martin (1981). 
This is the case in the crocodylomorph, Sphcnosuchus, where the 
remainder of the posterior articulation is of squamosal origin. 
Eopneumatosuchus resembles eusuchians in lacking a prootic con- 
tribution to the posterior articulation. It has no cotyle, but also 
lacks a deeply interdigiting suture. 

In Lesothosuchus the posterior articular area is shaped like an 
inverted pear. It is crushed somewhat towards the midline so that 
it is separated from the quadrate. The articulation is underlain 
and medially undercut by a pneumatic cavity in the otoccipital. 
The corresponding part of the quadrate is badly damaged. There 
was, presumably, a bony knob on the quadrate to fit the cotyle, 
but it is not preserved. 

The facies articularis posterior is more extensive in eusuchians 
than in the Triassic forms. The lateral part of the eusuchian occi- 
put has two distinct otoccipital/ quadrate articulations — a laterally- 
directed articulation lying beneath the foramen for the hyo- 
mandibular ramus of the facial nerve and the temporal artery (the 



“cranio-quadrate canal” of Iordansky, 1973), and a ventral ly-di- 
rected articulation on the paroccipital process. The parocciput 
extends dorsal and lateral to the foramen and is overlain by the 
squamosal. Only the ventral part of this articulation appears to 
be homologous with the facies articularis posterior of Lesotho- 
suchus. In Lesothosuchus the quadrate has a more vertical orienta- 
tion than in Recent taxa. It articulated with the otoccipital bone 
ventral to the hyomandibular ramus, which lay in an open groove 
over the dorsal surface of the posterior cotvlus. This is assumed 
to be the primitive situation for the Crocodylia. Eusuchians have 
extended the quadrate dorsally and ventrally relative to this, so 
that it contacts the lateral margins of the parocciput dorsally and 
the basicranium ventrally. In addition, the eusuchian quadrate 
has regained a posterior articulation with the squamosal, just an- 
terior to the lateral end of the paroccipital process. The extension 
of the posterior articulation in eusuchians mirrors the increased area 
of quadrate fixation found anteriorly, both being modifications for 
complete akinesis. 

In Lesothosuchus the body of the quadrate is hollow and is 
perforated by many foramina. These pneumatic foramina resemble 
those of Orthosuchus and differ from those of Protosuchus and 
eusuchians in being randomly situated all along the dorsal surface 
of the quadrate. Although only a small part of the ventral surface 
of the quadrate is preserved, it is perforated also. One foramen 
connects the tympanic cavity with the superior temporal fossa. 

There are at least three possible explanations for the unusual 
quadrate morphology. If the structure of the quadrate represents 
an elaboration of quadrate pneumaticity found in eusuchians, the 
quadrate of Lesothosuchus could have carried an extensive si- 
phonium from the tympanic cavity into the lower jaw. Alterna- 
tively, the cavity in the quadrate could simply be an extensive 
periotic sinus, an analog to the pneumatic cavities in the braincase. 
The first hypothesis would not account for the ventral perforation 
of the quadrate unless the siphonium of Lesothosuchus was in some 
manner connected to the eustachian system. Neither hypothesis 
would explain the foramen which extends into the superior tem- 
poral fossa. 

A third possibility is suggested by comparison with birds, the 
other surviving archosaur derivative. In the approximate position 
of the fenestrated quadrate of Lesothosuchus , birds have a temporal 
rete, an anastomosis between the stapedial artery and the lateral 
head vein (Saiff, 1974, 1976, 1978, in press; Crow and Crow, 1979). 
Relative to the condition in birds and other archosaurs, Lesotho- 
suchus and other crocodilians have extended their quadrates antero- 
dorsally so that this region is covered by the quadrate. In Recent 
crocodilians the stapedial artery is reduced, the temporal artery is 



enlarged and has a posterior origin, and there is no temporal rete. 
All of these vascular changes may he the result of the separation 
of the tympanic recess from the orbit and temporal fenestra as a 
consequence of the increase in the fixation area for the quadrate. 
Triassic taxa had a more open tympanic cavity and may have had 
a rete which passed through the quadrate. This would explain the 
ventral perforation of the quadrate and the presence of a foramen 
leading to the musculature of the temporal fossa. Interpreting the 
quadrate in this way presumes a more primitive cranial arterial 
system than in extant crocodilians, a more diffuse rete than in 
modern birds, and a rather sinuous course for the stapedial artery 
(since it would have to swing ventrally and medially under the 
postorbital bar to reach the orbit). While this option seems to 
provide the best explanation of the morphology observed in Leso- 
thosuchus , it is not necessarily an exclusive explanation. The ex- 
tensive hollow cavity indicates some degree of quadrate pneu- 
maticity and there is good reason to believe that the siphon ial sys- 
tem is an ancestral character in crocodilians. 

Associated with the tympanic cavity of Lesothosuchus are three 
periotic pneumatic cavities. The first of these, lying just dorsal to 
the posterior quadrate articulation, begins in a deep recess that is 
an extension of the middle ear cavity. The recess leads medially 
into two pneumatic foramina. The ventral foramen appears to be 
directed anteriorly to connect with an anterior sinus, but it has 
not been adequately prepared. The dorsal foramen is situated at 
or near the junction of the squamosal, prootic and otoccipital bones 
within the tympanic cavity (sutures are obscured in this area). 
It has been prepared to an internal pneumatic sinus at the medial 
junction of these same bones. Via the sinus, the tympanic cavity 
is connected to the posttemporal fenestra posteriorly and the su- 
perior temporal fenestra anteriorly. The sinus corresponds to the 
dorsal periotic sinus of eusuehians, the antrum pneumaticum dor- 
sale. In eusuehians that sinus is partially divided by a thin shelf 
of prootic bone so that the dorso-lateral portion, carrying the oc- 
e : pito-temporal and orbito-temporal arteries, is separated. This 
dorsal portion (“post-quadrate canal” of Walker, 1972) is weakly, 
if at all, pneumatic and has a lateral foramen at the junction of 
the squamosal, prootic, and otoccipital. The ventral part (“mastoid 
antrum” of Walker, 1972) is extensively pneumatic (much more 
than in Lesothosuchus) and has a separate lateral foramen at the 
junction of the prootic and otoccipital. Lesothosuchus and Spheno- 
suchus have only a single pneumatic sinus above the facies articu- 
laris posterior and the divided cusuehian sinus is obviously derived 
from it. 

Immediately ventral to the posterior eotvle is a deep pneumatic 
recess in the otoccipital which undercuts the articular facet. This 



sinus, the antrum pneumaticnm centrale (“caudale” of some au- 
thors) also occurs in cusuchians, where it is restricted to the otoc- 
cipital just below its articulation with the quadrate. In cusuchians 
it communicates with the dorsal sinus by a canal medial to the pos- 
terior quadrate articulation. In Lcsothosuchus the canal communi- 
cates with the medial recess which leads into the dorsal sinus. 

A third periotic sinus, the antrum pneumaticnm rostrale, is 
formed anterior to the foramen for the facial nerve (VII). It is a 
deep recess of the braincase wall which joins the tympanic cavity 
just dorsal to the foramen. Its lateral wall appears to be formed 
by the quadrate, but this area is incompletely preserved. Within 
the sinus are fine struts of bone between the braincase and quadrate. 
In Eopneumatosuchus the sinus is very highly strutted. It lies be- 
tween the facial foramen and the trigeminal foramen, a position 
which can be safely inferred in Lcsothosuchus. However, in 
Eopneumatosuchus the sinus lies under a lateral shelf of the prootic, 
which articulates with the quadrate. There is a similar shelf in 
Sphcnosuchus, although the recess is only weakly developed. The 
formation of the lateral wall of the sinus by the prootic may be 
the primitive condition in crocodilians. In Recent taxa the corre- 
sponding area is pneumatic, but not obviously so since it is un- 
strutted. It may be a prolongation of the middle ear into a gap 
between the anterior arm of the quadrate and the braincase wall, 
or it may be incorporated into the quadrate. In either case, it over- 
lies the eustachian system and the cavities in the basisphenoid 
which surround the cerebral carotid. 

The Lcsothosuchus specimen has the otic capsule lying medial 
to the facies articularis posterior. The endocranial component of 
the capsule is a swollen protrusion into the endocranial cavity. 
Internally, there is a distinct suture separating the prootic and 
otoccipital (opisthotic) parts of the capsule. Above this suture is 
the foramen for the endolymphatic duct. The supraoccipital (epi- 
otic) suture is not visible. The dorsal part of the endocranial cap- 
sule is constricted by the expansion for the cerebrum anteriorly 
and by the deep floccular recess posteriorly. Recent cusuchians 
differ from most higher archosaurs in lacking a floccular recess. 
Although the endocranial cavity of Lcsothosuchus seems small in 
comparison with Recent taxa, it is difficult to judge the cranial 
volume by the small amount of surface preserved. Anterior to the 
capsule is the foramen nervi facialis (VII), opening laterally into 
the rear of the rostral periotic sinus. 

Anterior and dorsal to the otic capsule and near the dorsal 
periotic sinus is a crack which Walker (1972) interpreted as the 
prootic/ opisthotic suture. This interpretation is not possible since 
the crack runs anterior to the otic capsule. 

The lateral part of the capsular region is not well preserved 



and mechanical preparation of the remaining matrix does not seem 
possible. The cochlea is completely enclosed by bone laterally, so 
that the fenestra ovalis can only be reached from above. This mor- 
phology requires a dorsally oriented stapes and oblique tympanum 
similar to those of Recent eusuchians. Nash (1975) restored Ortho- 
sucluis with a small, laterally oriented tympanum in the notch at 
the posterior corner of the skull roof. In light of the similarity of 
the tympanic region to Lesothosuchus , and the fact that the tym- 
panum of Recent forms always covers the dorsal pneumatic fora- 
mina in the quadrate, an oblique orientation seems likely for 
Orthosuchus as well. In Recent crocodilians the tympanum lies 
at an oblique angle over the inclined quadrate, extending laterally 
about one-third of the quadrate's length. It is completely enclosed 
by bone, but is separated from the squamosal at its posteromedial 
corner by connective and vascular tissues. In Lesothosuchus the 
orientation was presumably similar, but must have been more ex- 
tensive, laterally, to cover the dorsal foramina in the quadrate. One 
of these foramina is just anterior to the mandibular articulation. 
The posterior margin of the tympanum would have been on the 
quadrate and along soft tissues passing dorsal to the facies articu- 
laris posterior. There was probably some attachment to the squa- 
mosal on a crest at the rear of the tympanic cavity. 

At the anterior end of the tympanic region, part of the anterior 
wall of the quadrate is preserved. In a bit of matrix adjacent to 
this there is an elongate piece of bone which may be part of the 
quadratojugal, otherwise not preserved. A quadratojugal structure 
like that of Orthosuchus is likely for Lesothosuchus. Because of 
the proximity of the quadrate to the postorbital bar, the lower tem- 
poral fenestra would have been very small, especially with the 
quadratojugal inserted. This contrasts with the much larger fenes- 
trae of Orthosuchus and Eopncumatosuchus. 

Anterior to the foramen nervi facialis, only a small part of the 
side wall of the braincase is preserved. This includes the posterior 
part of the laterosphenoid and the anterior part of the prootic, 
which is recessed on its external surface to form the rostral pneu- 
matic sinus. The laterosphenoid lies between the quadrate and 
parietal at the antero-vcntral margin of the superior temporal 
fenestra. It is broken anterior and lateral to this, but the presence 
of a cotylus in the ventral surface of the postorbital indicates that 
the laterosphenoid had a dorsal knob of typical archosaurian design. 


Five vertebrae are preserved — one cervical, two dorsal, and two 
caudal. All of these, except for the posterior caudal, are platy- 
coelous (“amphicoelous” of some authors). In this respect the 
centra resemble those of other Triassic crocodilians. There are 



no pleurocoels. The neuro-central suture is fused in all vertebrae, 
another indication of the adult nature of the specimen. Measure- 
ments arc given in Table 1. 

The cervical vertebra (Fig. 4) is probably the 5th or 6th mem- 
ber of the presacra] series. There is a short cervical rib attached to 
the centrum at two points — on a short transverse process (diapo- 
physis) and at the anteroventral corner of the centrum (parapophy- 
sis). Hie “body” of the rib is directed anteroposteriorly as it is in 
Recent crocodilians. It is expanded anteriorly to form an articula- 
tion for the posterior extension of the preceding rib. The centrum 
above and below the parapophysis is excavated so that the para- 
pophysis is very prominent. The proportion of length to height 
for the centrum is 1.2; the proportion of length to width 1.2. The 
centrum bears a short keel on the midline of the ventral surface. 
The neural spine is narrow and posteriorly situated. The cervical 

Figure 4. — Lcsothosuchus charigi, A-C. Anterior views of cervical (pos- 
sibly 5th or 6th), dorsal (approximately 10th), and caudal (possibly 3rd or 
4th) centra. D, Block of crushed elements: anterior dorsal vertebra (ant. dor. 
vert. ); dorsal armor; ribs; right scapula. Scale is 1 cm. 



can be compared with that of Orthosiicluis, as figured by Nash 
(1975). Lesothosuchus differs from that genus by having a much 
lower neural arch and a relatively larger neural canal. 

The two dorsal vertebrae arc from the anterior and middle 
parts of the dorsal column. The anterior vertebra was badly 
crushed in a block containing part of a scapula, dorsal osteoderms, 
ribs and a caudal vertebra (Fig. 4). The anterior dorsal retains a 
ventral parapophysis on the centrum, but situated near the base 
of the pedicel. In all crocodilians the parapophysis migrates dor- 
sally along the centrum in the transitional series between “typical” 
cervical and dorsal vertebrae. After the first few dorsals the para- 
pophysis and diapophysis lie adjacent to each other on the trans- 
verse process, a condition found in the anterior dorsal of Lcsotho- 
suchus. Romer (1956) and Colbert (1952) considered this type 
of articulation to be a primitive archosaurian feature. Among 
archosaurs, I know it to be absent only in phytosaurs, theropod 
dinosaurs, and birds. In these taxa the parapophysis migrates dor- 
sally only as far as the pedicel of the neural arch. In Orthosuchus 
the first four dorsals retain a parapophysis which is at least partly 
on the centrum while Recent Alligator have a central parapophysis 
only on the first three dorsals. Judging from the position of this 
facet, the anterior dorsal of the type specimen of Lesothosuchus 
is probably the 9th, 10th, or 11th presacral. 

There is no ventral keel on the centrum of this anterior dorsal, 
a feature shared with Orthosuchus. The parapophysis is very large, 
much larger than that of the cervicals. The transverse process ex- 
tends directly outward and flares slightly to form an articulation 
for the rib tubercle. The spine is high, but relatively narrow. 
Orthosuchus differs from Lesothosuchus in having a much broader 
neural spine and a higher neural arch. 

When Lesothosuchus is compared with eusuchians and Ortho- 
suchus, , the more posterior dorsal vertebra appears to be from the 
middorsal region, approximately at the 19th presacral position. 
The centrum is somewhat elongate, with a length /height propor- 
tion of 1.5 and a length/ width proportion of 1.6. It is constricted 
in the midline. The parapophysis and diapophvsis are rather 
widely separated on the transverse process. The transverse process 
is much less extensive than those of eusuchian dorsals of compara- 
ble centrum width (Fig. 7). The height of the neural spine cannot 
be determined. This vertebra closely resembles that of comparable 
position in Orthosuchus. 

The two caudals are from the anterior and middle parts of the 
tail. The more anterior one corresponds to the third or fourth 
caudal. It is much larger than the anterior caudals of otherwise 
comparably sized eusuchians. The centrum is broadly flattened 
ventrallv, with large facets for the caudal chevrons. The rib is 



fused and posteriorly situated. The centrum is somewhat excavated 
laterally. The neural spine is incomplete, but vertically directed. 
Only a single, large chevron is preserved, and it also belongs to 
the anterior part of the caudal series. 

The more posterior caudal was removed from a block which 
contained the dorsal ostcoderms, dorsal ribs and the anterior dorsal 
vertebra. The centrum is biconvex, elongate, and ventrally flat- 
tened. The rib is posteriorly situated and prominent, but, relative 
to the anterior part of the caudal series, it has moved higher up 
on the pedicel of the arch. The neural spine is incompletely 

Pectoral appendage and girdle 

Of the shoulder girdle, only the dorsal end of the right scapula 
and the right coracoid are preserved. The end of the scapula is 
preserved in the block mentioned above (Fig. 4). It is expanded 
dorsally and constricts sharply to a narrow waist at the point of 

The shape of the coracoid is distinctively crocodilian (Fig. 5D). 
There is an expanded, “ procoraeoid” process, an elongate shaft 
with a distinct “waist,” and an expanded distal end. The coracoid 
compares well with Broom's (1904) figure of Notochcnnpsa and 
with Nash's (1971) figure of Orthosuchus, although the coracoid 
of Orthosuchus appears to have a less expanded distal foot and to 
be somewhat more massive. Lesothosuchus has a delicate coracoid 
which tapers to a thin edge anterior to the glenoid. This “pro- 
coracoid” area is piereed by a eoracoidal foramen. As in modern 
eusuchians, the proximal (humeral) end bears a flattened surface 
for articulation with the scapula. Because of the angle between 
this facet and the plane of the coracoid, the scapula would have 
been directed dorsally at an angle to the coracoid, as in Recent 

The glenoid facet on the posterior surface is directed backward 
into the coracoid (parasagittal) plane. This contrasts with cu- 
suchians and mesosuehians, which have an outwardly directed 
glenoid fossa (Fig. 5E). A parasagittal orientation of the glenoid 
fossa would have only allowed a stance in which the humerus was 
held close to the body, rather than directed outward in a sprawling 
position. This type of glenoid was once thought to be unique to 
the dinosaurs among archosaurs (Bakker and Galton, 1974). It is 
now known to be present in orthosuchids, Protosuchus , Pseudhes- 
perosuchus , Sphenosuchus and the thecodontian, “ Mandasuchus .” 
In none of these taxa is the direction of the glenoid demonstrably 
different from that of a “fully erect” dinosaur, such as Ilypsilo- 
phodon. The planes of orientation used in the following descrip- 



tion presume a parasagittal and nearly vertical orientation for the 
limbs, the primitively dorsal surface of the humerus being rotated 
to a posterior, and possibly somewhat lateral position; that of the 
femur to a medial position. 

Lcsothosuchus lacks a “biceps” tubercle on the lateral surface 
of the coracoid. Such a tubercle is present on coracoids of some 
theropods (Ostrom, 1976) and Sphenosuchus (Walker, 1972). The 
structure previously called the biceps tubercle in Archaeopteryx 
is probably the attachment for the furcula (Whetstone, Ms.). In 
the position of the tubercle, which probably served as the origin of 
the supracoracoideus muscle, the Lesotho specimen has a rugose 

Figure 5. — A-D, Lcsothosuchus charigi, BM (NH) R 8503: A-C, restora- 
tions of the left humerus at natural size; D, lateral view of right coracoid, x2; 
E, Alligator, juvenile coracoid, X^. 



ridge just anterior to the glenoid and sternal to the coracoid fora- 
men. Eusuchians have a similar rugosity. 

Of the forelimb, the left and right humeri and a left ulna were 
preserved. The humerus is long and slender, with somewhat less 
torsion than in eusuchians (Fig. 5A-C). It is difficult to compare 
the humeral torsion with Orthosuchus , since Nash’s restorations of 
that genus seem to have the distal end incorrectly placed. Lcso- 
thosuchus has an expanded humeral head that is convexly rounded 
and oval in cross section. The medial surface is set at a slight 
angle. Orthosuchus and eusuchians have a more flattened and less 
enlarged humeral head. Lcsothosuchus has a long deltoid crest, 
though incompletely preserved on both humeri of the type speci- 
men. The posterior surface of the distal extremity is more de- 
pressed than in eusuchians. The supracondylar ridges are pro- 
nounced. The distal articular surface is composed of two rounded 
condyles, separated by a groove. In Recent eusuchians the humeral 
condyles are well differentiated as part of a series of adaptations 
in the elbow which result in the distal movement of the radius, 
relative to the ulna, during forearm flexion (see Walker, 1972, 
1974). Lcsothosuchus lacks this condylar differentation. 

The ulna is slender, with compressed proximal and distal ends 
(Fig. 7C). It lacks the medial facet on the head that is critical to 
the operation of the “push-rod” mechanism discussed above. The 
proximal end is very unusual in having an egg-shaped knob on the 
lateral surface for articulation with the radius. Tin’s would have 
allowed an extensive rotation surface for that bone. Nothing com- 
parable is known among other archosaurs. The proximal articular 
surface consists of a depression on either side of the lateral knob. 
These depressions fit the condyles of the humerus. Orthosuchus 
and eusuchians differ from Lcsothosuchus in having poorly formed 
humero-ulnar articulations. By articulating the ulna with both 
humeral condyles, Lcsothosuchus has shifted the olecranon medi- 
ally under at least part of the medial condyle. It is unlikely, how- 
ever, that the ulna excluded the radius from that condyle since 
this would preclude pronation in a conventional humeral orienta- 
tion. The shaft of the ulna is slender, slightly curved and somewhat 
twisted. On the anterior surface of the distal end is a depressed, 
rugose insertion for the flexor carpi ulnaris. Just lateral to this ru- 
gosity is an elongate facet, the articulation for the medial corner 
of the radiale. This articulation is longer and more depressed than 
the corresponding structure in Recent crocodilians. 

Pelvic appendage 

The shaft and distal end of the left femur and the distal end 
of the right femur were recovered (Fig. 6G-J). The right shaft is 
broken just below the “fourth” trochanter. Judging from general 



„ ... 

'..W ' “ 



Figure 6 . — Lcsothosuchus charigi, BM (NH) R 8503: A, B, medial and 
lateral views of left dentary; C, D, posterior aspects of right and left humeri; 
E, proximal articular surface of left ulna; F, dorsal osteoderm; G-I, left femur 
in medial, posterior, and lateral aspects; J, portion of right femur; K, L, right 
and left second metatarsals. Scale is 1 cm. 



proportions found in other crocodilians, the length of the femur 
was at least 70 mm. The shaft is slightly built and strongly re- 
curved antero-posteriorly. The dorsal surface of the distal end 
bears two epicondylar ridges. The lateral and medial surfaces on 
either side of the epicondylar ridges are flattened. The medial sur- 
face bears a pronounced groove for the medial collateral liga- 
ments. There is a great disparity between the tibial and fibular 
condyles. The tibial condyle is more rounded, extends farther dis- 
tally and is lower dorso-ventrally. There is a deep intercondylar 
notch on the posterior surface with little articular surface connect- 
ing the two condyles. A similar morphology is present in Ortho- 

The fibular shaft is very slender and is sigmoidally curved in 
the antero-posterior plane. The proximal end is compressed. The 
distal end is slightly crushed, but appears to have been more com- 
pressed than in eusuchians. The fibula of Orthosuchus is only fig- 
ured in anterior and posterior aspects by Nash but it is shorter 
and much more massive than that of Lesothosuclius (Fig. 7). 
Little can be said of the metatarsals (Fig. 6) and phalanges. They 
do not differ significantly from the corresponding elements in 
Orthosuchus or eusuchians. 

Ribs and Osteoderms 

Two dorsal ribs are preserved. One is an anterior rib with 
broadly separated head and tubercle. It is unusual in the degree 
of dorso-vcntral compression of the vertebral processes. The shaft 
expands distally, but is incomplete. The more posterior rib is long 
and slender. The proximal end is not adequately exposed for 

The ribs were associated with four dorsal osteoderms, pre- 
served so that none is completely exposed (Fig. 4, 6F). Two ap- 
pear to be complete, but are crushed into each other so that the 
dorsal surface is not visible. The outline of these bones resembles 
the dorsal armor of Orthosuchus . The plates are rectangular, 
slightly curved dorso-ventrally and have an anterior peg, pre- 
sumably to underlie the preceding plate. There is no indication 
of a lateral flange, but this may be the result of breakage. One 
incomplete scute has the dorsal surface exposed. The sculpture of 
fine pits and ridges is similar to that on the skull roof. This sculp- 
ture is quite distinct from that on the dorsal osteoderms of Ortho- 
suchus, which has large, deep pits. There is a thickened, unsculp- 
tured ridge on the leading edge of the plate, which marks the 
overlap of the preceding plate. 

Four smaller plates are presumably from the caudal region. 
They lack anterior processes, but have a thickened leading edge. 
A curious element of uncertain position has a size and sculpture 



Figure 7. — Mid-dorsal vertebra, left ulna (left figure) and right fibula 
(right figure) of A. juvenile Alligator ; B. Orthosuchus stonnhergi (after Nash 
1975); C. Lcsothosuclius charigi ; all X 1 to show the proportions of meso- 
podials to the width of the dorsal centrum. The arrow indicates the position 
of the rounded articulation for the radius. 



similar to the small osteoderms, but is a thickened wedge. It could 
be interpreted as part of the ventral fold armor under the limbs, 
but since the related Orthosuchus lacks ventral armor, the bone 
remains indeterminate. 


Mode of Life 

A striking feature of the type specimen of Lesothosuchus is the 
long and slender build of the limbs. This is even more apparent 
when the limbs are compared with an extant eusuchian of com- 
parable body size. Because of the incomplete state of the vertebral 
column, it is not possible to express the relative length of the 
limbs in terms of presacral length. Instead, I have used the width 
of the 19th presacral centrum. Because of the weight-bearing 
function of the dorsal vertebrae, the vertebral width seems, in- 
tuitively, to be a satisfactory indicator of body size. Comparative 
indices for limbs of Lesothosuchus , Orthosuchus , and some Recent 
crocodylids are given in Table 2. Lesothosuchus is dramatically 
different in its limb proportions; even from the closely related 
Triassic Orthosuchus . This limb elongation raises questions re- 
garding the locomotor pattern of Lesothosuchus and other Triassic 

Modern crocodilians are able to assume a variety of stance and 
gait postures beyond the resting “sprawl” by which they have been 
stereotyped. When moving overland, the limbs are usually shifted 
into the parasagittal plane and the body lifted up from the 
ground. This “high walk” has been figured by Schaeffer (1941). 
Cott (1961) has described another method of locomotion whereby 
small crocodiles gallop or hop in the maimer of a squirrel. Still 

Table 2. — Limb lengths of some Triassic and Recent crocodilians expressed 
as a proportion of dorsal vertebral width. 

chart gi 

( type ) 

( typo ) 























* Indices are limb lengths divided by the width of the 19th presacral centrum. 
In Lesothosuchus the exact position of the vertebra can not be known with 
certainty, but the width of the centrum varies little in this region. Data for 
Orthosuchus are from Nash (1975); data for Stcgomosuchus from Emerson 
and Loomis (1904). The presacral width is used in the indices for 
Stcgomosuchus. Indices of Recent crocodilians reflect the range of indices 
obtained on all taxa available in the collections of the British Museum 
(Natural History). 



another possibility is full bipcdality (Cliarig, 1972). In recogni- 
tion of these varied locomotor postures and their improvement 
over the classic sprawl of lower tetrapods, Cliarig (1972) has 
termed the crocodyloid stance and gait “semi-improved.” By in- 
ference based upon skeletal comparisons, he further applied this 
terminology to the early crocodilians and pseudosuchians. Chang’ s 
approach to pseudosuchian locomotion was quite sound and long 
overdue. However, the analogy from modern forms may not be 
applicable to all of the Triassic crocodilians. 

Orthosuchus differs from eusuchians in almost every feature of 
the hindlimb which Cliarig (1972) used to separate the semi-im- 
proved and “erect” (parasagittal) archosaurs: the acetabulum is 
deep and perforate (though not fully open, it is as open as the 
bipedal Archaeopteryx); the supra-aeetabular crest is well devel- 
oped; there is ample origin for the protractor musculature on the 
anterior iliac crest (which extends considerably anterior to the 
acetabulum) and on the elongate, anteriorly directed pubis; and 
the femur has a well developed, medially directed head (though 
it lacks a distinct neck). Nash (1971) correspondingly restored 
Orthosuchus with an erect gait. 

Lesothosuchus was presumably similar to Orthosuchus in the 
morphology of the femur and hip, but differs from Orthosuchus 
and Recent crocodilians in other aspects of limb morphology. The 
limbs are relatively more slender and elongate, as discussed above. 
The humeral head is expanded and convex, increasing the degree 
of movement possible at the shoulder. The deltopectoral crest is 
long, increasing the vertical backswing leverage (Bakker and Gal- 
ton, 1974). The ulna has eotyles for articulation with both humeral 
condyles, increasing the structural stability of the elbow, but de- 
creasing or eliminating ulnar rotation. There is a unique condyle 
on the ulna for articulation with the radius, increasing the rotational 
capacity of the radius. The limbs arc greatly elongated and lightly 
built, more so in the mesopodium than the propodium, and more 
in the hind limb than the forelimb. Lesothosuchus resembles 
Orthosuchus but differs from extant eusuchians in having the 
glenoid directed along the plane of the body. From the morphology 
of the shoulder girdle and limbs, it seems likely that Lesothosuchus 
held its limbs close to the body, in the parasagittal plane, as do 
most Recent mammals. 

All of these features would seem to be specializations for cur- 
sorial progression. This progression could have been by running 
(cursoriality in the strict sense) or by the bounding gallop ob- 
served in living forms by Cott (1961). Walker (1970) has sug- 
gested that the latter mode of locomotion was primitive for the 
Croeodylia and that the customary sprawl of extant forms is a sec- 
ondary adaptation to an amphibious lifestyle. The differences be- 



tween the limb girdles of protosuchians and higher eroeodilians do 
indicate that their method of locomotion was quite different. Lull 
(1953) argued that Stegomosuchus , with proportionally shorter 
limbs than Lesothosuchus, was a small cursorial predator with para- 
sagittal limb posture. Although this may be the adaptive zone into 
which the earliest eroeodilians radiated, it is necessary to reconcile 
this mode of life with the cranium, whose morphology indicates 
the presence of an operculum (Ohrklappe) and an oblique tym- 
panum. In recent taxa these have generally been interpreted as 
adaptations for swimming. Considering the graeile build of spheno- 
suchids, the primitive “outgroup” for comparison with Triassie 
eroeodilians, it is difficult to accept an aquatic mode of life for the 
earliest eroeodilians. It seems likely that the otic structures must 
have evolved as a result of other factors. It is possible that the 
oblique tympanum was originally a consequence of akinesis, while 
the external ear functioned for sound reception, as it does in 

Relationships of Lesothosuchus 

Lesothosuchus resembles Stegomosuchus in the shape of the 
superior temporal fenestrae, but differs greatly in the proportions 
of the limbs to the skull roof and vertebral centra, and the relative 
size of the dorsal armor. The type specimen of Stegomosuchus 
preserves few other features for comparison. Lesothosuchus differs 
from Orthosuchus in many features: the shape and size of the 
temporal fenestrae, the structure of the occiput, lateral margin of 
the squamosal, cervical vertebrae, anterior dorsal vertebrae, cora- 
coid, humerus, ulna and fibula, the length of the limbs relative to the 
vertebrae and skull roof, and the sculpture of the dorsal armor. 
However, it shares with Orthosuchus the highly fenestrated quad- 
rate and the absence of a posterior notch on the dentary for the 
mandibular foramen, both of these features are unique to them 
among the Croeodylia (see Crompton and Smith, 1980, for Proto- 
suchtis). These two genera comprise the new subfamily Ortho- 

Orthosuchines and Protosuchus share features presumed to be 
primitive for the Croeodylia, despite spotty distributions among 
the comparative outgroups: laterally directed orbits, superficial 

postorbital bar, two palpebral bones, primary palate, loose posterior 
quadrate articulation, platyeoelous centra, anterior iliac crest, supra- 
aeetabular ridge, and elongate, rod-like pubis. These characteristics 
partly diagnose the grade, “Protosuehia.” 

With eusuehians and mesosuehians, Lesothosuchus shares ad- 
vanced skeletal features which are not present, as a group, in 
pseudosuehians or proterosuehians: the postorbital bone antero- 
posteriorly reduced; the parietals fused; the supratemporal fossa 



anteromedially placed so that it lies over, rather than alongside 
the brainease (enlargement of the fossa in mesosuchians is pre- 
sumed secondary); the lateral wall of the inside of that fossa 
formed partly by the quadrate and laterosphenoid; the descending 
process of the squamosal lost; the quadrate strongly inclined, with 
two articular faces, sutured to the prootic, laterosphenoid, squa- 
mosal and postorbital, and pneumatic; the otic notch “closed” by 
the posterior articulation of the quadrate; periotic pneumatic cavi- 
ties developed; the squamosal forming a shelf over the otic re- 
gion; the posttemporal fenestra reduced; the supraoccipital ex- 
cluded from the foramen magnum; the internal carotid artery 
enclosed by bone posterior to its entrance into the otic region; the 
coracoid elongate, expanded sternally, and with a distinct waist. 
Features unknown for Lesothosuchus , but which are probably an- 
cestral for the Crocodylia, include: anterior supraorbital bone 

present; loss of serrations on the teeth; closure of the basal articu- 
lation in the skull by suture; enclosure of the eustachian tubes in 
the bones of the basieranium; loss of clavicles; elongation of the 
proximal carpals; and presence of a calcaneal heel. These features 
can be added to those above to complete my diagnosis of the 

Relationships of Sphenosuchus 

Sphenosuchus and its allies remain a problematical group which 
seems to be closely related to crocodilians. Their morphology can 
be variously interpreted as support for at least three phylogenetic 

Reversing his earlier opinion, Walker (1974) argued that Sphe- 
nosuchus was closer to birds than to crocodilians. The features 
that he used can be categorized as: 1) being absent in Spheno- 
suchus (e.g. streptostylic-kinetic system), 2) being common to 
ether “higher” archosaurs (e.g. elongate cochlear recess), 3) being 
absent in the earliest birds (e.g. elongate coracoids), or 4) being 
present in both birds and true crocodilians. Sphenosuchus does, 
however, share with birds the contribution of the prootic bone to 
the posterior quadrate cotyle, a feature which may be absent in 

Walker (1970) had originally placed Sphenosuchus closer to 
crocodilians. This relationship is supported by the presence of 
elongated proximal carpal bones in Sphenosuchus , Pseudhespero - 
suchus , and the undescribcd genus from the Welsh fissure deposits 
and the elongation of the dorsal process of the quadratojugal in 
Sphenosuchus . These characteristics are otherwise unique to croco- 
dilians. This phylogeny could also be supported by the “akinetic” 
skull of Sphenosuchus, an interpretation contrary to Walker’s 
(1974). Metakinensis, the presumed primitive condition in archo- 



saurs, is precluded in Sphenosuchus by the broad suturing of the 
occipital elements. Streptostyly, the avian condition, is not possi- 
ble in Sphenosuchus since the alinement of the two heads of the 
quadrate in the plane of the cheek and the elongation of the an- 
terior head of the quadrate would prevent the quadrate from rock- 
ing in its articulation. The anterior head forms a “stop” against 
streptostyly. Streptostyly is also prevented by the unbroken post- 
orbital bar. Sphenosuchus has the jugal and postorbital bones 
tightly sutured within the bar. Moreover, their contact is too 
vertical to allow them to slide apart with an appreciable antero- 
posterior vector, even if the contact were loose. The snout is held 
tightly together by squamous sutures which would prevent sliding 
as envisioned by Walker (1974). While these features preclude an 
avian-type intracranial joint, some slight movements may have 
been possible at the dorsal end of the quadrate, which retains ball 
and socket joints. 

Because of the substantial differences in the morphology of the 
quadrate and quadrate articulations between Sphenosuchus and 
croeodilians, it is difficult to evaluate the significance of akinesis 
as a functional similarity. There is also some doubt as to the primi- 
tive condition of the cranium in birds, which have generally been 
presumed to have retained an ancestral kinesis by shifting the 
joint progressively forward (Bock, 1964). Although Bock (1964) 
predicted that the braincase of Archaeopteryx would be meso- 
kinetic, new preparation of the London specimen of Archaeopteryx 
(Whetstone, 1983) shows that it is not. “Akinesis” as a character 
unifying Sphenosuchus and croeodilians is the result of a single 
shared morphology, the broad, tight suturing of the skull roof to 
the more posterior and ventral occipital elements, a feature which 
is also shared with birds. 

A third phylogenetic hypothesis, which I support, as detailed 
below, is that birds and croeodilians share a unique crocodylo- 
morph ancestry, with Sphenosuchus as a sister group. Although 
accepting this phylogenv requires that one accept the loss of elon- 
gate carpals in the avian stem, the weight of the cranial evidence 
may justify it. 

Origin of birds 

Walker (1972, 1974) was the first to suggest that birds and 
croeodilians have a common ancestry independent of dinosaurs. 
His argument was based upon comparisons between Sphenosuchus 
and Recent birds. There is now additional evidence to support a 
common-ancestor hypothesis in the cranial morphology of the 
earliest croeodilians and of Mesozoic and Recent birds. The de- 
tailed morphology of these birds and arguments regarding avian 
character polarity are presented in a separate paper (Whetstone, 



MS.). Lcsothosuchus shares many derived cranial features with 
primitive birds: a hollow quadrate bone; periotic pneumatic 

sinuses in the dorsal, central and rostral positions; a bipartite 
quadrate articulation with the braincase; an anterior articulation 
formed, at least in part, by the laterosphcnoid, squamosal and 
prootic; and a posterior cotyle for the quadrate at the anterior 
base of the paroeciput and formed, at least in part, by the otoccipi- 
tal. The structure and position of the paroccipital process may 
also be a shared derived feature at this level, but the character 
distribution is such that it is difficult to determine the primitive 
situation in birds. The detailed similarity in the construction of 
these features and their distribution in fossil archosaurs and birds 
strongly supports their homologous origin in an ancestor unique to 
both crocodilians and birds. This hypothesis is contrary to the 
popularly accepted theory of avian descent from carnivorous 
dinosaurs (Ostrom, 1976), a theory supported primarily by the 
structure of the carpus and maims in Archaeopteryx. 

The quadrate is hollow in most Recent birds, including the 
flightless ratites. This hollow cavity has a medial foramen connect- 
ing with the middle ear, an independent feature which is also 
shared with crocodilians, but which is probably convergcntly de- 
rived within the Avcs. Among Mesozoic birds, the quadrates of 
Archaeopteryx and Gobipteryx appear to be hollow, while those 
of the hesperornithids appear to be solid, a characteristic of many 
heavy-boned diving birds (e.g. penguins). Only Ichthyornis is 
known to have a medial pneumatic foramen. To the best of my 
knowledge a hollow quadrate bone lias never been described in a 
dinosaur, sphcnosuchid or thecodontian and none of these have 
medial pneumatic foramina. 

The primitive position of the antrum pneumaticum dorsale in 
crocodilians is between the supraoccipital, otoccipital, squamosal 
and parietal in that part of the cranium where all of these elements 
interconnect. The sinus connects with the middle ear just dorsal 
to the facies articularis posterior via a foramen at or near the junc- 
tion of the squamosal, prootic and otoccipital. The sinus and its 
lateral foramen have this structure in juveniles of most Recent 
birds and in the Mesozoic hesperornithiforms. Sphcnosuchus has 
a dorsal sinus but the details of its construction are as yet unde- 
scribed. This sinus is absent in both saurischian and ornithischian 
dinosaurs and in thecodontians. 

The antrum pneumaticum centrale of crocodilians is located 
in the base of the paroccipital process. In Lcsothosuchus it under- 
lies and medially undercuts the posterior cotylus for the quadrate. 
In Recent eusuchians the opening into the middle ear cavity is just 
ventral to the posterior quadrate articulation and immediately pos- 
terior to the fenestra ovalis. In most Recent birds the sinus has 



this same morphology, except that the foramen is bordered partly 
by the prootic. It is present in Hesperornis, and probably in 
Enaliornis. Only one dinosaur is known to develop a similar struc- 
ture, the ornithomimid, Gallimimus. In that genus the paroccipital 
process is hollow and has two anterior foramina (see figures 5 and 
6 by Osmolska et al. , 1972, where the foramina are misidentified 
as the fenestra ovalis and fenestra rotunda). This cavity does not 
underlie or undercut the quadrate articulation, which is a single 
cup in the squamosal situated near the lateral terminus of the 
paroccipital process. This morphology is apparently a convergence 
to that of birds or crocodilians. The theropods, AUosaurus, Droniae- 
osaurus, and Tyrannosaurus all lack the cavity, as do sphenosuchids 
and thecodontians. 

The antrum pneumaticum rostrale of early crocodilians, such 
as Eopneumatosuchus, is situated just anterior to the foramen for 
the facial nerve and posterior to the trigeminal foramen. It is 
overlain by an anterior process from the quadrate, and overlies 
the carotid and eustachian canals. This is also true of most modern 
birds, with the notable exception of penguins, which lack the 
cavity. Birds differ from crocodilians in that the lateral wall of 
the sinus is formed by the alasphenoid part of the parasphenoid, 
presumably an autapomorphy for birds. The sinus is present in 
hesperornithiforms, including the Lower Cretaceous Enaliornis. An 
antrum pneumaticum rostrale is absent in theocodontians and 
theropod dinosaurs, although the ornithischian Ilypsilophodon has 
a depression in the position of the sinus. 

Among the archosaurs, the quadrate articulation is bipartite only 
in sphenosuchids, crocodilians and birds. With the exception of 
the highly sutured phytosaurs, thecodontians and dinosaurs have a 
single socket for the quadrate which is formed by the squamosal 
bone. There is no contact with either the laterosphenoid or prootic. 
The squamosal extends laterally as far as the terminus of the 
paroccipital process and separates the quadrate from the otoeeipital. 
Essentially the same morphology is found in Sphenodon. The na- 
ture of the quadrate articulations in primitive birds have generally 
been misunderstood. This is because of the unfortunate descrip- 
tion of the quadrate as ‘one-headed’ and because of the fusion of 
otic elements in the adult skull. 

The facies artieularis anterior of primitive crocodilians is formed 
by the pr ootic, squamosal, laterosphenoid and postorbital. In ratites 
and the hesperornithids, it is formed by the prootic, squamosal 
and laterosphenoid. This is presumed to be the primitive situation 
for birds, although the laterosphenoid component is lost in most 
neognathous taxa. Birds and crocodilians are the only archosaurs 
that articulate the quadrate with the prootic and laterosphenoid. 



In Sphenosuchus the anterior articulation is formed only by the 
squamosal bone. 

Primitive birds ( Archaeopteryx , hesperornithids, ratites, and 
possibly penguins) resemble Lesotho su cl uis in having the facies 
articularis posterior as a cotyle situated at the anterior base of the 
paroccipital process. It is formed, at least in part, by the otoccipital. 
This cotyle is medially underlain and undercut by the central 
periotic sinus. New preparation of the London specimen of 
Archaeopteryx shows this articulation to be very similar to that of 
Lesothosuchus. In Ilesperornis and many Recent birds, there is a 
canal just medial to the cotyle which connects the dorsal and central 
periotic pneumatic cavities. 

Because Sphenosuchus lacks many of the unique homologies of 
birds and crocodilians, I consider it to be more remotely related 
to both groups. Sphenosuchus has a dorsal periotic sinus, but lacks 
central and rostral pneumatic sinuses. The quadrate articulation 
is bipartite as in birds and crocodilians. The posterior articulation 
is a cotyle, which is partly formed by the prootic, but not the 
otoccipital. The anterior articulation is formed by the squamosal 
only. The anterior articulation resembles that of birds in being a 
cotyle, but this is the primitive form of the primary (“squamosal”) 
articulation in arehosaurs. Martin, Stewart and Whetstone (1980) 
have shown that the dentitions of crocodilians and Mesozoic birds 
are unique among arehosaurs in having an unserrated crown with 
a constricted waist, and an expanded root with an oval, enclosed 
resorption pit. Sphenosuchus has a primitive, thecodontian-like 
dentition, with serrations, no waist, and straight roots. 

If one argues that birds and crocodilians are only remotely 
related, it would be necessary to interpret each of these features 
as convergence. This seems unlikely in light of the detailed struc- 
ture which is shared and the differences in mode of life between 
crocodilians and birds. When the alternative hypotheses are com- 
pared, the considerable cranial evidence favors a sister-group rela- 
tionship between birds, crocodilians and sphenosuchids (Fig. 8). 


For allowing me to examine specimens, I thank A. J. Charig, 
C. A. Walker, G. Cowles, N. Arnold and P. Crush (London); 
G. Viohl (Eichstatt); H. Jaeger and H. Fischer (Berlin); S. L. 
Olson and N. Hotton (Washington); A. D. Walker (Newcastle); 
E. S. Gaffney (New York); J. Ostrom (New Plaven); W. Turnbull 
and J. Bolt (Chicago); C. L. Forbes (Cambridge, England); B. J. 
Pyrah (Yorkshire); P. Calton (Bridgeport); A. Elzanowski and 
II. Osmolska (Warsaw) and L. D. Martin, W Duellman, R. Men gel, 
and M. J. Mengel (Kansas). I must particularly thank Dr. and 
Mrs. A. D. Walker for allowing me to stay at their home while in 



Newcastle. M. A. Klotz and C. D. Whetstone prepared some of 
the figures. A. D. Walker, E. O. Wiley, H. P. Schultze, and R. M. 
Mengel read the manuscript and made many helpful suggestions. 
Advice and encouragement from L. D. Martin and A. J. Charig 
were particularly appreciated. Funding was provided by NSF 
DEB 7821432, Sigma Xi, F. M. Chapman Fund, a Fulbright-Hays 
Fellowship, the National Geographic Society, and a Dissertation 
Fellowship from the University of Kansas. A. J. Charig, P. J. 
Whybrow, John Attrige, and lone Rudner were members of the 
field party which collected the type specimen. 


Figure 8 . — Phylogenetic hypothesis advocated by the author. Character 
suites in the skull which are discussed in the text are 1 ) antrum pneumaticum 
dorsale, bipartite quadrate articulation; 2) prootic and laterosphenoid con- 
tributing to anterior quadrate articulation, otoccipital contributing to posterior 
quadrate articulation, antrum pneumaticum rostrale and centrale, quadrate 
pneumaticity; 3) quadrate sutured to the braincase, anterior quadrate articu- 
lation extended dorsally, posterior portion of the carotid enclosed, prootic 
contribution to the posterior articulation lost (not known with certainty in 
Lesothosuchm ), basipterygoid articulation sutured (inferred in Lcsothosuchus 
by comparison with Orthosuchus). 




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